The present invention relates to a ball screw. Ball screws of this type have a spindle nut which is arranged rotatably on a threaded spindle, with balls being interposed.
Ball screws can be subdivided into those with inner deflection and those with outer deflection.
Where inner deflection is concerned, a plurality of ball chains are often provided which extend in each case over about 360 degrees. The ball track extends over about 360 degrees, that is to say winds approximately once about the axis of rotation. The spindle nut has arranged in it deflection inserts which deflect the ball chain from the end of the ball track towards its start and at the same time lift the balls over the thread flank of the threaded spindle.
Where outer deflection is concerned, the ball chain, that is to say the ball track, often extends over a plurality of turns; the deflection piece is often arranged outside the spindle nut and, according to the length of the ball chain, spans a number of turns, that is to say thread flanks.
A ball chain comprises a multiplicity of balls arranged in a row. Intermediate pieces may be arranged between balls adjacent to one another. Intermediate pieces and balls are arranged loosely one behind the other. The ball chain is arranged in a ball channel which is delimited by ball grooves formed on the spindle nut and on the threaded spindle. Arranging the ball chain in the ball channel ensures that the balls are arranged as a ball chain. Intermediate pieces of this type may also be designated as spacers or distance pieces.
DE 101 22 106 A1, for example, has disclosed a ball screw between the spindle nut (1) and threaded spindle (2) of which at least one ball chain (6,8) formed from balls (9) rolls in each case along a ball channel (5) which is delimited by ball grooves (3,4) formed on the spindle nut (1) and on the treaded spindle (2), the ball chain (6,8) being deflected from one end of the ball channel (5) to a start of this ball channel (5) in deflection portions of the ball channel (5). Intermediate pieces are arranged between balls adjacent to one another. Intermediate pieces of this type rule out contact between balls adjacent to one another and therefore reduce wear as a result of friction. Furthermore, the balls can be guided more effectively in order to maintain a satisfactory; ball chain.
Ball screws are used increasingly in power-assisted steering gears of motor vehicles. Noises caused by the cycle of movement of the balls in the ball channel may be troublesome. The reason for undesirable noises of this kind may be an excessive final pitch-circle play of the ball chain. This means that balls arranged adjacently to one another may have play with respect to one another in the direction of extent of the balls and, for example, may butt against one another. In the case of ball chains without intermediate pieces, this noise source may be especially troublesome.